At 09:23 AM 4/26/97 -0400, you wrote:
>>
>> Hi all!
>> Thanks  all for help.
>> To me was managed to erase the bit of protection UV eraser
>> during 3 hours and to record the new program.
>
>So it seems to me that this is the best way to do it. The code protect
>bit can be erased, but there is absolutely no way any part of the program
>will still be there (after 3 hours) once it is erased.
>
>This is good to know.
>
>
>
>BAJ
>
Maybe I'm old and I missed it but I have been lurking for the last few days
and I don't believe I saw anyone drop the magical reference "A" to the
discussion on the 16C74 protection bits.

It goes like this, the 16C74 (without the "A" suffix) can be erased and
reused after code protection BUT eraseure time for a protected device can
be 2 to 3 hours! Normally it is 10-20 minutes ball park without protection.

If the part is a 16C74"A" then it is "sudden death." If you write a "0" to
anyone of the multiple code protect bits then protection is enable and is
not UV erasable. Rather an expensive OTP!

Beware of any 14-bit core part with an "A" suffix plus all the NEW 14-bit
parts that don't have an "A" suffix. Of the later released PICs, only the
12C508/9 have not "featured" non UV erasable code protection.

A good rule of thumb to remember:

Any 14-bit part that has both an "A" and a non "A" variant, then the non
"A" variant can be safely code protected and erased. (However these devices
are obsolete and being phased out.)

Examples 16C64, 16c64A, 16C74, 16C74A, 16C62, 16C62A, 16C73, 16C73A, 16C65,
16C65A


14-bit devices without an "A" variant all feature unerasable code protect
bits.
Examples: 16C63, 16C72, 16C66, 16C67, 16C76, 16C77, 16Cxxx, 12C6xx


Two exceptions to the above rule are 16C71, 16C61, both are ok to protect.

Jim